Green’s Dictionary of Slang

1. one who runs an illicit distillery.

1906		A.H. Lewis Confessions of a Detective 42: I’d clamber up a fire-escape, or steal along a hall, or creep across a roof, until I’d located the still and collared my chemist.
1962		cited in Allsopp Dict. Carib. Eng. Usage.

2. (N.Z. prison) a manufacturer of illcit drugs.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 41/1: chemist n. a person [...] good at manufacturing drugs.